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Re: [Qemu-discuss] Supported hypervisors running VMs in nested VM

From: Bandan Das
Subject: Re: [Qemu-discuss] Supported hypervisors running VMs in nested VM
Date: Tue, 6 Oct 2015 23:07:41 -0400

> On Oct 6, 2015, at 4:43 PM, Rain Maker <address@hidden> wrote:
> Unfortunately, no difference. WIth or without -hypervisor doesn't make
> any difference to that flag.
> But, experimenting on, I found something <very> odd.
> The 0x3a register is 0 when the VM boots up.
> Even when I start a L2 VM, 0x3a is still 0.
> However, once I start WITH -enable-kvm, 0x3a is suddenly 5(!). See
> this terminal session, which is executed within the L1 VM ("kvmtest").
> http://storage4.static.itmages.com/i/15/1006/h_1444163503_6656916_6ffbfd2352.png
> I was only executing mini.iso (an Ubuntu Netinstaller), and closing it
> at the boot prompt. I did not do anything in the L2 VM. Both the Qemu
> VM as the -enable-kvm VMs do boot.
> Is this how the MSR is supposed to react?
> AFAIK, the MSR can only be modified from kernelspace (which also
> explains why Qemu would only reset it with -enable-kvm, there are no
> kernelspace components used without it if I understand correctly)
> Looking at this, I can imagine that Windows does not detect a correct
> value. It will get 0. Would it make sense to cygwin KVM and see if
> that changes the MSR register?

You have to use kvm to run (hardware assisted) nested virtualization. I am not 
sure why you think Windows will read 0 for the feature control msr but you have 
use —enable-kvm in L0 when you are launching L1 (Hyper-V in your case). When L1 
runs L2,
you don’t have to worry about using —enable-kvm. Hyper-V should automatically 
detect available
hardware features available to it and attempt to enable hardware virtualization.
> Sincerely,
> Roel Brook.
> 2015-10-05 23:17 GMT+02:00 Bandan Das <address@hidden>:
>> Rain Maker <address@hidden> writes:
>>> Qemu on Linux works fine. I did not even have to explicitly set
>>> -hypervisor. It simply works.
>> Sorry, I meant running Linux with "-hypervisor" to see if specifying
>> that is somehow messing with the feature flags.
>>> As does VirtualBox FYI.
>>> Booting with UEFI didn't make any difference.
>>> After A LOT of Googling, I believe that Hyper-V actually checks bit
>>> 0x3a of the MSR register (instead of, as the error would .
>>> This is a 3 bit register (IA32_FEATURE_CONTROL). Within my VM, the
>>> value returned by rdmsr is "0", while on my host it is "5". For
>> That seems odd. Even Linux wouldn't work if that value is 0.
>>> Hyper-V to work (from what I understand), it should be either 4 or 5.
>>> Googling that, funny enough, brought me back to this list:
>>> https://lists.gnu.org/archive/html/qemu-devel/2015-01/msg01371.html.
>>> I guess it really IS important to know what you're googling for to
>>> find things fast...
>>> That thread simply says that the kernel is too old. Well, my host is
>>> running 4.2, so should be new enough.
>>> I'm a bit stuck. Any ideas?
>>> Sincerely,
>>> Roel Brook
>>> 2015-10-05 21:18 GMT+02:00 Bandan Das <address@hidden>:
>>>> Rain Maker <address@hidden> writes:
>>>>> Thanks Bandan.
>>>>> That helped a bit. It got me to the next hurdle, as you suspected.
>>>>> I modified the virsh XML so that -cpu host,+vmx,-hypervisor is passed,
>>>>> and the installation now reports "Hyper-V cannot be installed because
>>>>> virtualization support is not enabled in the BIOS.".
>>>> Thanks for trying this out.
>>>>> I am sure that vmx is passed. but "systeminfo" does report "Hyper-V
>>>>> cannot be installed because virtualization support is not enabled in
>>>>> the BIOS."
>>>>> Apparently, Microsoft queries the BIOS to verify that the
>>>> When kvm is initialized, it checks for TXT and VMX both being enabled.
>>>> That too, only if the feature control msr is locked. I don't think there
>>>> are actually any specific "bios calls" to find this out. I would assume
>>>> Hyper-V should be doing the same thing but your testing says otherwise.
>>>> Can you please run linux as L1 with "-hypervisor" and see if it works ?
>>>> If it doesn't, please check dmesg for relevant messages.
>>>> Thanks,
>>>> Bandan
>>>>> virtualization bit is actually enabled, instead of simply relying on
>>>>> the VMX flag.
>>>>> Unfortunately, VMs are still not starting either. The seabios in Qemu
>>>>> seems to be pretty difficult to modify. I'll check whether I can
>>>>> reinstall on UEFI, maybe that is going to make a difference.
>>>>> The way VMWare does this is actually semi-documented (it hasn't always
>>>>> been in the product, and a workaround involving manually editing the
>>>>> configuration has been used for a long time). I'll see if I can
>>>>> correlate these to Qemu options, to see whether we can use those
>>>>> instructions to get this working on Qemu.
>>>>> 1. Set 'vhv.enable = "TRUE" on the VM
>>>>>  It "enables virtual hardware virtualization". This seems equivalent
>>>>> to the -hypervisor flag
>>>>> 2. Set 'monitor.virtual_exec = "hardware" on the VM.
>>>>>  This option seems to force hardware virtualization for both CPU and
>>>>> MMU. Unsure whether there's an equivalent Qemu configuration option.
>>>>> Unsure whether it's needed on Qemu. Details at
>>>>> http://www.vmware.com/files/pdf/perf-vsphere-monitor_modes.pdf
>>>>> 3. Set hypervisor.cpuid.v0 = “FALSE” in the VM configuration
>>>>>  This seems synonymous to the +vmx flag
>>>>> 4. Enable the option to "Virtualize VT-x/EPT or AMD/RVI"
>>>>>  I have not found any option to explicitly do this in Qemu. Looking
>>>>> at my Ubuntu VM, the "ept" flag IS passed to the VM, so this should be
>>>>> OK.
>>>>> 5. Add the following CPU mask Level ECX: ---- ---- ---- ---- ---- ---- 
>>>>> --H- ----
>>>>>  Not sure how to do that in Qemu or what it does. Looking at
>>>>> https://en.wikipedia.org/wiki/CPUID, it seems to disable the XSAVE
>>>>> instruction(?). For fun, I passed -cpu ...-xsave, but it did not seem
>>>>> to make any difference whatsoever.
>>>>> Sincerely,
>>>>> Roel Brook
>>>>> 2015-10-04 5:07 GMT+02:00 Bandan Das <address@hidden>:
>>>>>> ...
>>>>>>> Windows 2012 / 2016 technical preview 3
>>>>>>> --------------------------------------------------------
>>>>>>> The installation via the "default" method of Add/Remove Features does
>>>>>>> not work. Hyper-V displays the error message "A hypervisor is already
>>>>>>> running".
>>>>>>> This check can be skipped by using a different method of installation
>>>>>>> (from PowerShell):
>>>>>>> Enable-WindowsOptionalFeature –Online -FeatureName Microsoft-Hyper-V
>>>>>>> –All -NoRestart
>>>>>>> This results in (again) the server booting up, but being unable to run
>>>>>>> any guest VMs. The error message is less clear then that in 2008, just
>>>>>>> "The Virtual Machine Management Service failed to start the virtual
>>>>>>> machine 'New Virtual Machine' because one of the Hyper-V components is
>>>>>>> not running (Virtual machine ID
>>>>>>> 0C063B29-249A-41C8-8A5B-6D4D2E37EF7C)."
>>>>>>> is what I could find.
>>>>>>> Other
>>>>>>> --------
>>>>>>> Just to verify that "nesting" is actually working, I've also installed
>>>>>>> a Ubuntu 15.10 VM and installed Qemu on it.
>>>>>>> This combination CAN successfully run a VM.
>>>>>>> I've also installed VirtualBox on one of the Windows VMs. This
>>>>>>> VirtualBox instance is also capable of running virtual machines.
>>>>>>> According to the icon in the bottom right, VirtualBox IS using the
>>>>>>> hardware virtualization.
>>>>>>> Is this a problem specific to Hyper-V? Is there a method to get
>>>>>> Nesting a Hyper-V L1 hypervisor is largely untested. But one of the 
>>>>>> problems I recollect is that Hyper-V doesn’t like running in a 
>>>>>> virtualized environment. It checks the “hypervisor” feature flag that 
>>>>>> Qemu exports. You could try running qemu with “-cpu  host,-hypervisor” 
>>>>>> or something similar and see if it makes any difference. I suspect there 
>>>>>> would be other roadblocks though, this is just one of them.
>>>>>>> Hyper-V working including running guests? I know for a fact that
>>>>>>> VMWare Workstation / ESX is able to run Hyper-V fully, so it should
>>>>>> Yes, IIRC one of the things ESX does is hide the hypervisor flag 
>>>>>> specifically for Hyper-V.
>>>>>> Bandan
>>>>>>> not be completely impossible (but I dislike VMWare for different
>>>>>>> reasons).
>>>>>>> My Qemu command line (generated by virt-manager). Except for disks and
>>>>>>> domain names, all are identical:
>>>>>>> qemu-system-x86_64 -enable-kvm -name Windows_2008_R2 -S -machine
>>>>>>> pc-i440fx-vivid,accel=kvm,usb=off -cpu
>>>>>>> SandyBridge,+invtsc,+osxsave,+pcid,+pdcm,+xtpr,+tm2,+est,+smx,+vmx,+ds_cpl,+monitor,+dtes64,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme
>>>>>>> -m 2048 -realtime mlock=off -smp 2,sockets=2,cores=1,threads=1 -uuid
>>>>>>> 54a8f3a3-66c2-45a5-a280-ecf7019a67fa -no-user-config -nodefaults
>>>>>>> -chardev 
>>>>>>> socket,id=charmonitor,path=/var/lib/libvirt/qemu/Windows_2008_R2.monitor,server,nowait
>>>>>>> -mon chardev=charmonitor,id=monitor,mode=control -rtc
>>>>>>> base=localtime,driftfix=slew -global kvm-pit.lost_tick_policy=discard
>>>>>>> -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=1 -global
>>>>>>> PIIX4_PM.disable_s4=1 -boot strict=on -device
>>>>>>> ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x6.0x7 -device
>>>>>>> ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x6
>>>>>>> -device 
>>>>>>> ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x6.0x1
>>>>>>> -device 
>>>>>>> ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x6.0x2
>>>>>>> -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -drive
>>>>>>> file=/sub/kvm/Windows_2008_R2.qcow2,if=none,id=drive-ide0-0-0,format=qcow2,cache=unsafe,aio=threads
>>>>>>> -device 
>>>>>>> ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1
>>>>>>> -drive 
>>>>>>> file=/sub/ISO/en_windows_server_2008_r2_with_sp1_x64_dvd_617601.iso,if=none,id=drive-ide0-0-1,readonly=on,format=raw
>>>>>>> -device ide-cd,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1
>>>>>>> -netdev tap,fd=24,id=hostnet0 -device
>>>>>>> rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:7b:d7:d2,bus=pci.0,addr=0x3
>>>>>>> -chardev pty,id=charserial0 -device
>>>>>>> isa-serial,chardev=charserial0,id=serial0 -chardev
>>>>>>> spicevmc,id=charchannel0,name=vdagent -device
>>>>>>> virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0
>>>>>>> -device usb-tablet,id=input0 -spice
>>>>>>> port=5903,addr=,disable-ticketing,seamless-migration=on
>>>>>>> -device 
>>>>>>> qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vgamem_mb=16,bus=pci.0,addr=0x2
>>>>>>> -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device
>>>>>>> hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev
>>>>>>> spicevmc,id=charredir0,name=usbredir -device
>>>>>>> usb-redir,chardev=charredir0,id=redir0 -chardev
>>>>>>> spicevmc,id=charredir1,name=usbredir -device
>>>>>>> usb-redir,chardev=charredir1,id=redir1 -chardev
>>>>>>> spicevmc,id=charredir2,name=usbredir -device
>>>>>>> usb-redir,chardev=charredir2,id=redir2 -chardev
>>>>>>> spicevmc,id=charredir3,name=usbredir -device
>>>>>>> usb-redir,chardev=charredir3,id=redir3 -device
>>>>>>> virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x7 -msg timestamp=on
>>>>>>> Thank you in advance for response.
>>>>>>> Sincerely,
>>>>>>> Roel Brook

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